Developing cartridge capable of releasing meshing between gear and rack gear

ABSTRACT

A developing cartridge includes: a casing; a developing roller; a developing electrode; a gear; a rack gear including a protrusion; and a cam having first and second cam surfaces. The rack gear meshes with the gear and is movable in a direction from one end toward another end of the casing. The cam is movable from a first position to a second position. The first cam surface of the cam at the first position contacts the protrusion, and causes the cam to move to the second position as the rack gear moves in the direction in a state where the first cam surface is in contact with the protrusion. A second cam surface moves the developing electrode in a direction away from the cam different from moving directions of the rack gear and the cam while contacting the developing electrode as the cam moves to the second position.

CROSS REFERENCE TO RELATED APPLICATION

This application is a reissue of U.S. Pat. No. 10,042,282, which wasfiled as U.S. patent application Ser. No. 15/715,979 and filed on Sep.26, 2017, and which claims priority from Japanese Patent Application No.2016-256106 filed Dec. 28, 2016. The entire content of the Japanesepriority application is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a developing cartridge including adeveloping roller.

BACKGROUND

Conventionally, a developing cartridge includes a detection protrusionfor moving an actuator positioned at a main body casing of an imageforming apparatus. The detection protrusion has a gear. The detectionprotrusion is rotatable around a shaft. The actuator is moved by thedetection protrusion pushing the actuator during rotation of the gear.Further, the gear has a toothless portion. In a case where the toothlessportion faces a drive gear that transmits the drive force to the gear,meshing between the gear and the drive gear is released. As a result,the rotation of the gear stops. As the rotation of the gear stops, therotation of the detection protrusion also stops.

SUMMARY

Meanwhile, in the above-described developing cartridge, it has beendesired to release meshing between a gear other than the gear and thedrive gear.

In view of the foregoing, it is an object of the disclosure to provide adeveloping cartridge capable of releasing meshing between a gear otherthan the gear and the drive gear.

In order to attain the above and other objects, according to one aspect,the disclosure provides a developing cartridge including: a casing; adeveloping roller; a developing electrode; a gear; a rack gear; and acam. The casing is configured to accommodate toner therein. Thedeveloping roller is rotatable about a first axis extending in an axialdirection. The developing roller is positioned at one end of the casing.The developing electrode is electrically connected to the developingroller. The gear is rotatable about a second axis parallel with thefirst axis. The rack gear meshes with the gear. The rack gear is movablein a direction from the one end of the casing toward another end of thecasing opposite to the one end of the casing. The rack gear includes aprotrusion. The cam is movable from a first position to a secondposition. The second position is farther away from the casing than thefirst position is from the casing in the axial direction. The cam has: afirst cam surface; and a second cam surface. The first cam surfacecontacts the protrusion in a case where the cam is at the firstposition. The first cam surface causes the cam to move from the firstposition to the second position in a case where the rack gear moves inthe direction from the one end of the casing toward the another end ofthe casing in a state where the first cam surface is in contact with theprotrusion. The second cam surface moves the developing electrode in adirection away from the cam while contacting the developing electrode ina case where the cam moves from the first position to the secondposition. The direction away from the cam is a direction different froma moving direction of the rack gear and a moving direction of the cam.

According to another aspect, the disclosure provides a developingcartridge including: a casing; a developing roller; a gear; a developingelectrode; a rack gear; a cover; and a cam. The casing is configured toaccommodate toner therein. The developing roller is rotatable about afirst axis extending in an axial direction. The developing roller ispositioned at one end of the casing. The gear is rotatable about asecond axis extending in the axial direction. The developing electrodeis electrically connected to the developing roller. The rack gear ismovable from the one end of the casing toward another end of the casingopposite to the one end of the casing. The rack gear is movable in adirection from the one end of the casing toward the another end of thecasing in accordance with rotation of the gear by meshing with the gear.The rack gear includes a protrusion. The cover covers at least a portionof the rack gear. The cover has an opening through which the developingelectrode is exposed to an outside. The cam is movable from a firstposition to the second position. The second position is farther awayfrom the casing than the first position is from the casing in the axialdirection. The cam has: a first cam surface; and a second cam surface.The first cam surface has a first edge and a second edge. The secondedge is positioned farther away from the casing than the first edge isfrom the casing in the axial direction. The first cam surface isinclined so that the first edge is positioned downstream relative to thesecond edge in a moving direction of the protrusion. The first camsurface causes the cam to move from the first position to the secondposition by engaging with the protrusion. The first cam surface ispositioned outside of a movement locus of the protrusion in a case wherethe cam is at the second position. The second cam surface is movabletogether with the first cam surface. The second cam surface ispositioned farther away from the casing than the first cam surface isfrom the casing in the axial direction. The second cam surface ismovable while contacting the developing electrode. The second camsurface has a fifth edge and a sixth edge. The sixth edge is positionedfarther away from the casing than the fifth edge is from the casing inthe axial direction. The second cam surface is inclined so as toprotrude toward the opening in a direction from the sixth edge towardthe fifth edge.

According to still another aspect, the disclosure provides a developingcartridge including: a casing; a developing roller; a gear; a rack gear;a cam; a spring; a cover; and a developing electrode. The casing isconfigured to accommodate toner therein. The developing roller isrotatable about a first axis extending in an axial direction. Thedeveloping roller is positioned at one end of the casing. The gear isrotatable about a second axis parallel with the first axis. The rackgear meshes with the gear. The rack gear is movable in a direction fromthe one end of the casing toward another end of the casing opposite tothe one end of the casing. The cam is movable from a first position to asecond position. The second position is farther away from the casingthan the first position is from the casing in the axial direction. Thecam includes a protrusion. The spring urges the cam from the firstposition toward the second position. The cover has an opening. Thedeveloping electrode is electrically connected to the developing roller.The developing electrode is movable together with the cam. Thedeveloping electrode has a second cam surface. The second cam surfacehas a fifth edge and a sixth edge. The sixth edge is positioned fartheraway from the casing than the fifth edge is from the casing in the axialdirection. The second cam surface is inclined so as to protrude towardthe opening in a direction from the sixth edge toward the fifth edge.The rack gear has: a first holding surface contacting the protrusion tohold the cam at the first position; and a second holding surfacecontacting the protrusion to hold the cam at the second position.

BRIEF DESCRIPTION OF THE DRAWINGS

The particular features and advantages of the embodiment(s) as well asother objects will become apparent from the following description takenin connection with the accompanying drawings, in which:

FIG. 1 is a perspective view of a developing cartridge according to afirst embodiment as viewed from one end side thereof in an axialdirection;

FIG. 2 is a perspective view of the developing cartridge according tothe first embodiment as viewed from the other end side thereof in theaxial direction;

FIG. 3 is an exploded perspective view of components at the other end ofthe developing cartridge according to the first embodiment;

FIG. 4 is a perspective view of a rack gear of the developing cartridgeaccording to the first embodiment as viewed from a rack gear portionside thereof;

FIG. 5 is an exploded perspective view of a gear cover of the developingcartridge and components accommodated therein according to the firstembodiment;

FIG. 6 is a perspective view of a cam of the developing cartridgeaccording to the first embodiment;

FIG. 7 is a perspective view illustrating a structure at the other endside of the developing cartridge according to the first embodiment, fromwhich the gear cover is omitted;

FIGS. 8A through 8D are cross-sectional views of an engaging portionbetween the rack gear and the cam taken along a plane orthogonal to anup-down direction according to the first embodiment, illustratingmovements of the rack gear and the cam;

FIGS. 9A and 9B are cross-sectional views of the rack gear, the cam, anda developing electrode taken along a plane orthogonal to a directionfrom one end to the other end of a casing of the developing cartridgeaccording to the first embodiment, illustrating movements of the rackgear, the cam, and the developing electrode;

FIG. 10 is a perspective view illustrating a structure at the other endside of a developing cartridge according to a second embodiment, fromwhich a gear cover is omitted;

FIGS. 11A and 11B are a perspective view of each components of thedeveloping cartridge according to the second embodiment, in which FIG.11A is an exploded perspective view of the gear cover and componentsaccommodated therein and FIG. 11B is a perspective view of a rack gearas viewed from a rack gear portion side thereof;

FIGS. 12A through 12C are cross-sectional views of an engaging portionbetween the rack gear and a cam taken along a plane orthogonal to theup-down direction according to the second embodiment, illustratingmovements of the rack gear and the cam; and

FIGS. 13A and 13B are cross-sectional views of the rack gear, the cam,and a spring electrode taken along a plane orthogonal to a directionfrom one end to the other end of a casing of the developing cartridgeaccording to the second embodiment, illustrating movements of the rackgear, the cam, and the spring electrode.

DETAILED DESCRIPTION First Embodiment

A developing cartridge according to a first embodiment will be describedwith reference to FIGS. 1 through 9B, wherein like parts and componentsare designated by the same reference numerals to avoid duplicatingdescription.

As illustrated in FIG. 1 , a developing cartridge 1 mainly includes acasing 11, a developing roller 12, a supply roller 15 (see FIG. 3 ), anagitator 14, and a coupling 13. The casing 11 accommodates tonertherein. In the following description, an axial direction of thedeveloping roller 12 will also be simply referred to as an “axialdirection”.

The developing roller 12 is a roller that supplies toner to anelectrostatic latent image formed on a photosensitive member (notillustrated). The developing roller 12 is rotatable about a first axisX1 extending in the axial direction. The developing roller 12 has ashaft 12A extending in the axial direction. The developing roller 12 ispositioned at one end E10 of the casing 11in, where the end E10 isdefined relative to a direction that extends from the shaft 12A toward ashaft 14A of the agitator 14 described later.

The supply roller 15 is a roller that supplies toner to the developingroller 12. The agitator 14 is a member that agitates the toner insidethe casing 11.

The coupling 13 is a member that receives a driving force from outside.Specifically, in a case where an input member (not illustrated) capableof advancing and retracting is provided at a main body casing (notillustrated) of an image forming apparatus (not illustrated) and theinput member advances and enters the coupling 13 to engage with thecoupling 13 in a rotational direction, the driving force is inputtedinto the coupling 13 from the input member. The driving force inputtedinto the coupling 13 is transmitted to the developing roller 12 via agear mechanism (not illustrated) and is also transmitted to the supplyroller 15 and the agitator 14.

The coupling 13 is positioned at one end of the casing 11 in the axialdirection. In other words, the coupling 13 is positioned opposite to adeveloping electrode 20 (see FIG. 2 , described later), with the casing11 interposed therebetween. That is, the coupling 13 is positioned at aside wall of the casing 11 opposite to a side wall 11A of the casing 11at which the developing electrode 20 is positioned.

As illustrated in FIG. 2 , the developing cartridge 1 further includes adeveloping electrode 20. The developing electrode 20 is positioned atthe other end of the casing 11 in the axial direction. The developingelectrode 20 is provided for moving an actuator AC positioned at themain body casing of the image forming apparatus. The actuator AC ispivotally movably supported to the main body casing. The actuator AC isconstituted by an electrically-conductive member. The image formingapparatus includes a power supply portion (not illustrated) and anoptical sensor (not illustrated). The power supply portion and theoptical sensor are positioned at the main body casing of the imageforming apparatus. The power supply portion supplies electric power tothe actuator AC. The optical sensor detects pivotal movement of theactuator AC.

As the driving force inputted into the coupling 13 is transmitted to thedeveloping electrode 20 through the gear mechanism and the agitator 14(see FIG. 1 ), the developing electrode 20 moves in an orthogonaldirection orthogonal to the axial direction. Specifically, theorthogonal direction is a direction of lifting the actuator AC upward.In other words, the driving force inputted into the coupling 13 istransmitted from the one end to the other end of the casing 11 in theaxial direction by the shaft 14A of the agitator 14.

As illustrated in FIG. 3 , the developing cartridge 1 includes anagitator gear 31 as an example of a gear, a bearing 40, a rack gear 50,a gear cover 60 as an example of a cover, and the developing electrode20. The agitator gear 31, the bearing 40, the rack gear 50, the gearcover 60, and the developing electrode 20 are positioned at the otherend of the casing 11 in the axial direction. The casing 11, the agitatorgear 31, the rack gear 50, and the gear cover 60 are made of anon-electrically-conductive resin.

The developing electrode 20 and the bearing 40 are made of anelectrically-conductive material. Specifically, the developing electrode20 and the bearing 40 are made of an electrically-conductive resin. Theelectrically-conductive resin is, for example, a polyacetal resincontaining carbon powder.

The agitator gear 31 is mounted to the other end portion of the shaft14A of the agitator 14. The agitator gear 31 is rotatable about a secondaxis X2 parallel with the first axis X1. The agitator gear 31 rotatestogether with the shaft 14A of the agitator 14. That is, the agitatorgear 31 rotates together with the developing roller 12 by the drivingforce inputted into the coupling 13.

The bearing 40 is a member for rotatably supporting the shaft 12A of thedeveloping roller 12 and a shaft 15A of the supply roller 15. Thebearing 40 includes a plate-like portion 41, a first bearing portion 42,a second bearing portion 43, and two first guide portions 44.

The plate-like portion 41 is a plate-like portion that extends in thedirection from the shaft 12A toward the shaft 14A. Specifically, theplate-like portion 41 extends from the shaft 12A of the developingroller 12 toward the agitator gear 31. The plate-like portion 41 ispositioned, in the axial direction, between the side wall 11A at theother end of the casing 11 in the axial direction and the rack gear 50.

Specifically, the plate-like portion 41 is positioned in a recessedportion 11B positioned at an outer surface of the side wall 11A. Hence,an outer surface of the plate-like portion 41 and the outer surface ofthe side wall 11A are substantially flush with each other (see FIG. 7 ).

The first bearing portion 42 is a hollow cylindrical portion thatrotatably supports the shaft 12A of the developing roller 12. The firstbearing portion 42 protrudes from the plate-like portion 41 in adirection away from the casing 11 in the axial direction. Specifically,the first bearing portion 42 protrudes farther than the second bearingportion 43 in the direction away from the casing 11 in the axialdirection.

The second bearing portion 43 is a hollow cylindrical portion thatrotatably supports the shaft 15A of the supply roller 15. The secondbearing portion 43 protrudes from the plate-like portion 41 in thedirection away from the casing 11 in the axial direction. The secondbearing portion 43 is positioned at a position closer to the agitatorgear 31 than the first bearing portion 42 is to the agitator gear 31.

Each of the first guide portions 44 is a portion that movably supportsthe rack gear 50 in a direction from the one end E10 of the casing 11(described later) toward the other end E20 of the casing 11. The twofirst guide portions 44 are provided so as to interpose the rack gear 50therebetween. Each of the first guide portions 44 supports the rack gear50. Each of the first guide portions 44 protrudes from the plate-likeportion 41 in the direction away from the casing 11 in the axialdirection. Each of the first guide portions 44 has a plate shapeorthogonal to the plate-like portion 41. Each of the first guideportions 44 has a first length in the direction from the one end E10 ofthe casing 11 toward the other end E20 of the casing 11, and a secondlength in the axial direction. The first length is greater than thesecond length. Each of the first guide portions 44 is positioned at aposition closer to the agitator gear 31 than the second bearing portion43 is to the agitator gear 31.

The casing 11 includes a second guide portion 11C, a third guide portion11D, and a fourth guide portion 11E. The second guide portion 11C, thethird guide portion 11D, and the fourth guide portion 11E each movablysupport the rack gear 50 in the direction from the one end E10 of thecasing 11 toward the other end E20 of the casing 11. The second guideportion 11C is positioned opposite to the third guide portion 11D andthe fourth guide portion 11E with respect to the rack gear 50. Thesecond guide portion 11C spans a range from the third guide portion 11Dto the fourth guide portion 11E and extends in the direction from theone end E10 of the casing 11 toward the other end E20 of the casing 11.

The third guide portion 11D and the fourth guide portion 11E face asurface of the rack gear 50 facing the agitator gear 31. The third guideportion 11D is positioned at a position closer to the developing roller12 than the agitator gear 31 is to the developing roller 12. The fourthguide portion 11E is positioned opposite to the third guide portion 11Dwith respect to the agitator gear 31 in the direction from the one endE10 of the casing 11 toward the other end E20 of the casing 11.

The rack gear 50 is movable in the direction from the one end E10 of thecasing 11 toward the other end E20 of the casing 11 opposite to the oneend E10. The rack gear 50 includes a main body portion 51, a rack gearportion 52, and a first protrusion 53 and a second protrusion 54 as anexample of a protrusion.

The main body portion 51 has a rectangular plate shape that is elongatedin the direction from the one end E10 of the casing 11 toward the otherend E20 of the casing 11. The rack gear portion 52 has a plurality ofgear teeth meshing with the agitator gear 31. The main body portion 51extends in a moving direction of the rack gear 50. The rack gear portion52 and the respective protrusions 53 and 54 protrude from a surface ofthe main body portion 51 facing the agitator gear 31. The rack gear 50is configured to move in the direction from the one end E10 of thecasing 11 toward the other end E20 of the casing 11 only while the rackgear portion 52 is meshed with the agitator gear 31. The rack gear 50 isconfigured to stop moving in a case where meshing between the rack gearportion 52 and the agitator gear 31 is released. That is, the rack gear50 is movable in the direction from the one end E10 of the casing 11toward the other end E20 of the casing 11 as the agitator gear 31rotates.

The rack gear portion 52 is positioned at a downstream portion of themain body portion 51 in the moving direction of the rack gear 50 in anend portion of the main body portion 51 closer to the casing 11 in theaxial direction. Specifically, the rack gear portion 52 is positioned atthe main body portion 51 at a region from an end portion of the mainbody portion 51 closer to the agitator gear 31 in the moving directionof the rack gear 50 to a center portion of the main body portion 51 inthe moving direction of the rack gear 50 (see FIG. 4 ).

The first protrusion 53 and the second protrusion 54 are positioned atpositions different from the rack gear portion 52 in the movingdirection of the rack gear 50. The first protrusion 53 and the secondprotrusion 54 are positioned at positions different from the rack gearportion 52 in the axial direction. Specifically, the first protruion 53and the second protrusion 54 are positioned at the main body portion 51at positions farther from the casing 11 than the rack gear portion 52 isfrom the casing 11 in the axial direction. Further, the first protrusion53 and the second protrusion 54 are positioned at positions closer tothe developing roller 12 than the rack gear portion 52 is to thedeveloping roller 12 in the moving direction of the rack gear 50. Morespecifically, the first protrusion 53 is positioned in the vicinity ofthe center portion of the main body portion 51 in the moving directionof the rack gear 50. The second protrusion 54 is positioned at an endportion of the main body portion 51 closer to the developing roller 12in the moving direction. The first protrusion 53 and the secondprotrusion 54 are capable of contacting a first cam surface 73A and athird cam surface 74A of a cam 70 (see FIG. 6 , described later) inaccordance with the movement of the rack gear 50.

The gear cover 60 covers the agitator gear 31 and the rack gear 50. Asillustrated in FIG. 5 , the gear cover 60 covers the cam 70, thedeveloping electrode 20, and a compression coil spring SP as an exampleof a spring. The cam 70 moves in the axial direction by receiving aforce applied from the rack gear 50. The cam 70 is made of anon-electrically-conductive resin. The compression coil spring SP ismade of an electrically-conductive material, specifically, metal.

The gear cover 60 includes a first cover portion 61, a second coverportion 62, and a third cover portion 63. The first cover portion 61covers the rack gear 50 and the agitator gear 31. The second coverportion 62 covers the cam 70 and the developing electrode 20. The thirdcover portion 63 covers the compression coil spring SP. The first coverportion 61 is elongated in the direction from the one end E10 of thecasing 11 toward the other end E20 of the casing 11 so that the rackgear 50 can be covered by the first cover portion 61 before, while, andafter the rack gear 50 moves.

The second cover portion 62 protrudes away from the casing 11 in theaxial direction. The second cover portion 62 protrudes away from asubstantially center portion of the first cover portion 61in, where thesubstantially center portion of the first cover portion 61 is definedrelative to the direction from the one end E10 of the casing 11 towardthe other end E20 of the casing 11. The second cover portion 62 has aninternal space that is in communication with an internal space of thefirst cover portion 61. Further, the second cover portion 62 has anopening 62A through which the developing electrode 20 is exposed tooutside.

The third cover portion 63 has a through-hole 63A penetrating thethickness of the third cover portion 63 in the axial direction. Thecompression coil spring SP is positioned inside the through-hole 63A.The third cover portion 63 is positioned at a position substantially thesame as the second cover portion 62 in the direction from the one endE10 of the casing 11 toward the other end E20 of the casing 11. Thethird cover portion 63 protrudes from the first cover portion 61 in adirection away from the rack gear 50. The through-hole 63A is opentoward the developing electrode 20.

Incidentally, in the present embodiment, a hollow portion of the thirdcover portion 63 is positioned between an outer peripheral surface ofthe third cover portion 63 and the through-hole 63A. However, the hollowportion may not be positioned between the outer peripheral surface ofthe third cover portion 63 and the through-hole 63A.

The cam 70 is positioned in the second cover portion 62 of the gearcover 60 so as to be movable in the axial direction. The cam 70 ismovable between a first position illustrated in FIG. 8A and a secondposition illustrated in FIG. 8B. The second position is farther awayfrom the casing 11 than the first position is from the casing 11 in theaxial direction. As illustrated in FIG. 6 , the cam 70 includes a baseportion 71, a rib 72, a first cam portion 73, a third cam portion 74, aprotruding portion 75, and two second cam portions 76.

The base portion 71 is a plate-like portion orthogonal to a direction inthat the rack gear 50 and the cam 70 face each other. The base portion71 has a first length in the axial direction, and a second length in thedirection from the one end E10 of the casing 11 toward the other end E20of the casing 11. The first length is greater than the second length.The rib 72 protrudes toward the rack gear 50 from an end portion of thebase portion 71 closer to the casing 11.

The first cam portion 73 and the third cam portion 74 are positionedbetween the rib 72 and the protruding portion 75. The first cam portion73 and the third cam portion 74 protrude from the base portion 71 towardthe rack gear 50.

The first cam portion 73 is positioned at a position different from thethird cam portion 74 in the moving direction of the rack gear 50.Specifically, the first cam portion 73 is positioned farther away fromthe agitator gear 31 in the moving direction of the rack gear 50 thanthe third cam portion 74 is from the agitator gear 31. The first camportion 73 diagonally extends from the protruding portion 75 toward therib 72. That is, the first cam portion 73 diagonally extends downstreamin the moving direction of the rack gear 50 from the protruding portion75. The first cam portion 73 has one end connected to the protrudingportion 75, and the other end separated from the rib 72. An intervalbetween the other end of the first cam portion 73 and the rib 72 isgreater than a diameter of each of the protrusions 53 and 54 of the rackgear 50.

The first cam portion 73 has a first cam surface 73A that is inclinedrelative to the moving direction of the rack gear 50. The first camsurface 73A is a surface for moving the cam 70 in the direction awayfrom the casing 11 in the axial direction. The first cam surface 73A isconfigured to contact the protrusions 53 and 54 of the rack gear 50 in acase where the cam 70 is at the first position. The first cam surface73A is configured to move the cam 70 from the first position to thesecond position. Specifically, in a case where the rack gear 50 moves inthe direction from the one end E10 of the casing 11 toward the other endE20 of the casing 11 in a state where the first cam surface 73A is incontact with the first protrusion 53 or the second protrusion 54, thefirst cam surface 73A causes the cam 70 to move from the first positiontoward the second position. In other words, the first cam surface 73Acauses to move the cam 70 from the first position to the second positionby engaging with the protrusions 53 and 54. In a case where the cam 70is at the second position, the first cam surface 73A is positionedoutside of a movement locus of the protrusions 53 and 54.

The first cam surface 73A is inclined so that a downstream edge of thefirst cam surface 73A in the moving direction of the rack gear 50 ispositioned closer to the casing 11 than an upstream edge of the firstcam surface 73A in the moving direction of the rack gear 50 is to thecasing 11 in the axial direction. Specifically, the first cam surface73A has a first edge E1, and a second edge E2. The second edge E2 ispositioned farther away from the casing 11 than the first edge E1 isfrom the casing 11 in the axial direction. The first cam surface 73A isinclined so that the first edge E1 is positioned downstream relative tothe second edge E2 in the moving direction of the rack gear 50.

The third cam portion 74 diagonally extends from a substantially centerportion of the rib 72 in the direction from the one end E10 of thecasing 11 toward the other end E20 of the casing 11 toward theprotruding portion 75. That is, the third cam portion 74 diagonallyextends downstream in the moving direction of the rack gear 50 from thesubstantially center portion of the rib 72. The third cam portion 74 hasone end connected to the rib 72, and the other end separated from theprotruding portion 75. An interval between the other end of the thirdcam portion 74 and the protruding portion 75 is greater than thediameter of each of the protrusions 53 and 54 of the rack gear 50.

The third cam portion 74 has a third cam surface 74A that is inclinedrelative to the moving direction of the rack gear 50. The third camsurface 74A is a surface for moving the cam 70 in a direction toward thecasing 11 in the axial direction. The third cam surface 74A isconfigured to contact the protrusions 53 and 54 of the rack gear 50 in acase where the cam 70 is at the second position. In other words, thethird cam surface 74A is positioned within the movement locus of theprotrusions 53 and 54 in a case where the cam 70 is at the secondposition. The third cam surface 74A is configured to move the cam 70from the second position toward the first position. Specifically, in acase where the rack gear 50 moves in the direction from the one end E10of the casing 11 toward the other end E20 of the casing 11 in a statewhere the third cam surface 74A is in contact with the first protrusion53 or the second protrusion 54, the third cam surface 74A causes the cam70 to move from the second position toward the first position.

The third cam surface 74A is positioned downstream relative to the firstcam surface 73A in the moving direction of the rack gear 50. The thirdcam surface 74A is positioned at a position different from the first camsurface 73A in a moving direction of the cam 70. Specifically, the firstcam surface 73A is positioned farther away from the casing 11 than thethird cam surface 74A is from the casing 11 in the axial direction.

The third cam surface 74A is inclined so that a downstream edge of thethird cam surface 74A in the moving direction of the rack gear 50 ispositioned farther away from the casing 11 than an upstream edge of thethird cam surface 74A in the moving direction of the rack gear 50 isfrom the casing 11 in the axial direction. Specifically, the third camsurface 74A has a third edge E3, and a fourth edge E4. The fourth edgeE4 is positioned farther away from the casing 11 than the third edge E3is from the casing 11 in the axial direction. The third cam surface 74Ais inclined so that the fourth edge E4 is positioned downstream relativeto the third edge E3 in the moving direction of the rack gear 50.

The protruding portion 75 protrudes toward the developing electrode 20from a portion of the base portion 71 farther from the casing 11. Theprotruding portion 75 protrudes toward the first cam portion 73 from oneend of the base portion 71 farther from the casing 11 in the axialdirection. The protruding portion 75 has a rectangular-shapedthrough-hole 75B penetrating the thickness of the protruding portion 75in the axial direction.

Each of the second cam portions 76 protrudes toward the developingelectrode 20 from a surface of the protruding portion 75 that faces thedeveloping electrode 20. Hereinafter, the surface of the protrudingportion 75 that faces the developing electrode 20 will also be referredto as “first surface 75A”. Each of the second cam portions 76 ispositioned spaced apart from each other in the axial direction. Each ofthe second cam portions 76 is positioned away from one end and the otherend of the protruding portion 75 in the axial direction. Each of thesecond cam portions 76 has a second cam surface 76A inclined relative tothe axial direction, and a support surface 76B for supporting thedeveloping electrode 20.

The second cam surface 76A is a surface for moving the developingelectrode 20 in a direction away from the cam 70 in a case where the cam70 moves from the first position to the second position. In a case wherethe cam 70 moves from the first position to the second position, thesecond cam surface 76A contacts the developing electrode 20. Thedirection away from the cam 70 is a direction different from the movingdirection of the rack gear 50 and the moving direction of the cam 70.The second cam surface 76A is movable together with the first camsurface 73A. The second cam surface 76A is positioned farther away fromthe casing 11 than the first cam surface 73A is from the casing 11 inthe axial direction.

The second cam surface 76A is inclined toward the first cam surface 75A.A downstream edge of the second cam surface 76A in the direction awayfrom the casing 11 in the axial direction is positioned closer to thefirst surface 75A than an upstream edge of the second cam surface 76A inthe direction away from the casing 11 in the axial direction is to thefirst surface 75A. Specifically, the second cam surface 76A has a fifthedge E5, and a sixth edge E6. The sixth edge E6 is positioned fartheraway from the casing 11 than the fifth edge E5 is from the casing 11 inthe axial direction. The second cam surface 76A is inclined so as toprotrude toward the developing electrode 20 in a direction from thesixth edge E6 toward the fifth edge E5. In other words, the second camsurface 76A is inclined so as to protrude toward the opening 62A in thedirection from the sixth edge E6 toward the fifth edge E5. The supportsurface 76B extends parallel with the first surface 75A.

Referring back to FIG. 5 , the developing electrode 20 is movablysupported at the second cover portion 62 of the gear cover 60. Thedeveloping electrode 20 is positioned at the first surface 75A of thecam 70. The developing electrode 20 is movable between a third positionand a fourth position. The fourth position is farther away from the cam70 than the third position is from the cam 70. The developing electrode20 has a substantially rectangular parallelepiped electrode portion 21,a first flange portion 22, and a second flange portion 23. The firstflange portion 22 and the second flange portion 23 protrude, in adirection away from the electrode portion 21 in the axial direction,from an end portion of the electrode portion 21 opposite to a secondsurface 21A (described later) of the electrode portion 21.

The electrode portion 21 is positioned so as to protrude through theopening 62A of the second cover portion 62 in the direction away fromthe cam 70 (see FIG. 3 ). Specifically, a protruding amount of theelectrode portion 21 from the opening 62A is greater in a case where thedeveloping electrode 20 is at the fourth position than in a case wherethe developing electrode 20 is at the third position.

The electrode portion 21 has a surface opposite to a surface of theelectrode portion 21 facing the cam 70. Hereinafter, the surface of theelectrode portion 21 opposite to the surface of the electrode portion 21facing the cam 70 will also be referred to as “second surface 21A”. Thesecond surface 21A is an arcuate curved surface that protrudes in thedirection away from the cam 70 in a cross-section orthogonal to theaxial direction. The electrode portion 21 has two recessed portions 24into which the two second cam portions 76 of the cam 70 can enter,respectively. The recessed portions 24 are configured to be recessedfrom the surface of the electrode portion 21 facing the cam 70 in thedirection away from the cam 70. Each of the recessed portions 24 has afourth cam surface 24A contacting the second cam surface 76A of thesecond cam portion 76, and a bottom surface 24B extending parallel withthe first surface 75A. The fourth cam surface 24A extends parallel withthe second cam surface 76A.

Of the surface of the electrode portion 21 facing the cam 70, a portionpositioned between the two recessed portions 24 serves as a supportedsurface 21B. In a case where the developing electrode 20 is at thefourth position, the supported surface 21B is supported at one of thesecond cam portions 76 of the cam 70 closer to the casing 11. Further, asurface of the first flange portion 22 facing the cam 70 serves as asupported surface 22A. In a case where the developing electrode 20 is atthe fourth position, the supported surface 22A is supported at the otherof the second cam portions 76 of the cam 70 positioned farther from thecasing 11. Incidentally, in a case where the developing electrode 20 isat the third position, at least one of the surfaces of the developingelectrode 20 facing the cam 70 (i.e. the surfaces including thesupported surfaces 21B and 22A) and the bottom surface 24B of eachrecessed portions 24 may be supported by the cam 70.

As illustrated in FIG. 7 , the compression coil spring SP is positionedbetween the electrode portion 21 of the developing electrode 20 and theplate-like portion 41 of the bearing 40 in the axial direction.Specifically, the compression coil spring SP has one end in contact withthe electrode portion 21 of the developing electrode 20, and the otherend opposite to the one end of the compression coil spring SP and incontact with the plate-like portion 41 of the bearing 40. Thus, thedeveloping electrode 20 is electrically connected to the developingroller 12 and the supply roller 15 through the compression coil springSP and the bearing 40.

More specifically, the compression coil spring SP is in contact with asurface of the electrode portion 21 closer to the casing 11.Accordingly, in a case where the developing electrode 20 is at the thirdposition, in a case where the developing electrode 20 moves from thethird position to the fourth position, and in a case where thedeveloping electrode 20 is at the fourth position, the compression coilspring SP keeps in contact with the electrode portion 21. That is, thedeveloping electrode 20 is movable while the developing electrode 20 isin contact with the compression coil spring SP.

The compression coil spring SP has a length in a case where the one endof the compression coil spring SP is in contact with the developingelectrode 20 and the other end of the compression coil spring SP is incontact with the bearing 40, and a natural length. The length is shorterthan the natural length. Further, the compression coil spring SP ispositioned opposite to the cam 70 with respect to the rack gear 50. Thecompression coil spring SP is positioned between the first guide portion44 and the second guide portion 11C in the direction from the one endE10 of the casing 11 toward the other end E20 of the casing 11.

Next, operations and effects of each member constituting the developingcartridge 1 will be described in detail. In a case where the developingcartridge 1 is in a brand-new state, the rack gear 50 is positioned at aposition closest to the one end E10 of the casing 11, and the cam 70 ispositioned at a position closest to the casing 11. With thisarrangement, the developing electrode 20 is placed at the thirdposition.

As illustrated in FIG. 2 , in a case where the developing cartridge 1 inthe brand-new state is attached to the main body casing of the imageforming apparatus, the second surface 21A of the developing electrode 20contacts an electrode provided at the actuator AC. Thus, the developingbias is supplied from a power source (not illustrated) of the imageforming apparatus to the developing electrode 20 through the electrodeof the actuator AC.

Thereafter, as a driving force is inputted from a driving source (notillustrated) at the main body casing to the coupling 13 of thedeveloping cartridge 1, the driving force is transmitted to the shaft14A of the agitator 14 through the coupling 13 and the gear mechanism(not illustrated). The driving force transmitted to the shaft 14A of theagitator 14 is transmitted to the agitator gear 31 as illustrated inFIG. 3 .

As the agitator gear 31 to which the driving force is transmittedrotates, the rack gear 50 moves in the direction from the one end E10 ofthe casing 11 toward the other end E20 of the casing 11. As illustratedin the sequence of FIGS. 8A and 8B, in a case where the first protrusion53 of the rack gear 50 contacts the first cam surface 73A of the cam 70to press the first cam surface 73A in accordance with the movement ofthe rack gear 50, the cam 70 moves in the direction away from the casing11 in the axial direction. In FIGS. 8A through 8D, a portion indicatedby hatching of dots represents a portion of the agitator gear 31 capableof meshing with the rack gear portion 52.

In a case where the cam 70 moves in the direction away from the casing11 in the axial direction, as illustrated in the sequence of FIGS. 9Aand 9B, the developing electrode 20 is pushed upward by each of thesecond cam surfaces 76A of the cam 70, and the developing electrode 20moves from the third position to the fourth position. That is, thedeveloping electrode 20 moves in the direction away from the cam 70, byreceiving a force from the cam 70 moving in the direction away from thecasing 11 in the axial direction.

In a case where the developing electrode 20 moves to the fourthposition, the actuator AC is pushed upward by the developing electrode20 and changed its position. That is, the cam 70 applies a force to theactuator AC through the developing electrode 20, thereby changing theposition of the actuator AC in one direction. Accordingly, the opticalsensor detects the change in position of the actuator AC in the onedirection. A control device of the image forming apparatus can determinethat the developing cartridge 1 is a brand-new cartridge, by detectingthe change in position of the actuator AC using the optical sensor.

As illustrated in the sequence of FIGS. 8B and 8C, in a case where therack gear 50 further moves in the direction from the one end E10 of thecasing 11 toward the other end E20 of the casing 11, the cam 70 moves inthe direction toward the casing 11 in the axial direction since thefirst protrusion 53 of the rack gear 50 presses the third cam surface74A of the cam 70. Thus, as illustrated in the sequence of FIGS. 9B and9A, the respective support surfaces 76B of the cam 70 are separated fromthe respective supported surfaces 21B and 22A of the developingelectrode 20, and the developing electrode 20 moves from the fourthposition to the third position. Incidentally, the movement of thedeveloping electrode 20 from the fourth position to the third positionmay be achieved by gravity, or may be achieved by a spring that urgesthe actuator AC.

Thereafter, as illustrated in the sequence of FIGS. 8C and 8D, in a casewhere the rack gear 50 further moves in the direction from the one endE10 of the casing 11 toward the other end E20 of the casing 11, thesecond protrusion 54 of the rack gear 50 sequentially presses therespective cam surfaces 73A and 74A of the cam 70. As a result, the cam70 moves in the direction away from the casing 11 in the axialdirection, and then, moves in the direction toward the casing 11 in theaxial direction. Therefore, in a case where the developing electrode 20returns to the third position after the developing electrode 20 moves tothe fourth position again, the optical sensor detects the change inposition of the actuator AC in one direction. That is, in thisembodiment, after the developing cartridge 1 in the brand-new state isattached to the main body casing of the image forming apparatus, theoptical sensor detects the change in position of the actuator in onedirection twice. This corresponds to the number of the protrusions 53and 54 of the rack gear 50. For example, in a case where the rack gear50 includes only one protrusion, the number of changes in position ofthe actuator in one direction detected by the optical sensor is one.Therefore, by setting the number of protrusions of the rack gear 50 inaccordance with the specification of the developing cartridge 1 (forexample, difference in an amount of toner accommodated in the developingcartridge 1), the control device can also determine the specification ofthe developing cartridge 1.

After the second protrusion 54 separates from the third cam surface 74Aas illustrated in FIG. 8D, meshing between the rack gear 50 and theagitator gear 31 is released. As a result, the transmission of thedriving force from the agitator gear 31 to the rack gear 50 is shut off,maintaining the developing electrode 20 at the third position.

According to the above, the following effects can be obtained in thisembodiment.

Since the rack gear 50 moves in the direction from the one end E10 ofthe casing 11 toward the other end E20 of the casing 11, meshing betweenthe rack gear 50 and the agitator gear 31 can be released.

Since the developing electrode 20 is formed of anelectrically-conductive resin, the shape of the developing electrode 20can be easily formed.

Second Embodiment

Next, a developing cartridge 101 according to a second embodiment willbe described with reference to FIGS. 10 through 13B, wherein like partsand components are designated by the same reference numerals as those ofthe first embodiment to avoid duplicating description. In the followingdescription, only parts differing from those of the above-describedfirst embodiment will be described in detail.

In the first embodiment, the compression coil spring SP is configured asa component separate from the developing electrode 20. However, in thesecond embodiment, a spring and the developing electrode 20 areintegrally configured as illustrated in FIG. 10 . Specifically, in thesecond embodiment, in addition to the casing 11, the agitator gear 31,and the bearing 40 similar to those of the first embodiment, thedeveloping cartridge 101 includes a rack gear 150, a cam 170 and aspring electrode 80 different from those of the first embodiment. Asillustrated in FIG. 11A, the cam 170 includes the base portion 71, theprotruding portion 75, a protrusion 77, and a spring support portion 78.The protrusion 77 and the spring support portion 78 of the cam 170 arenot included in the cam 70 according to the first embodiment, while thebase portion 71 and the protruding portion 75 of the cam 170 are similarto those of the cam 70 according to the first embodiment.

The protrusion 77 protrudes toward the spring electrode 80 from the endportion of the base portion 71 closer to the casing 11. The protrusion77 has a semi-circular columnar shape. A surface of the protrusion 77farther from the casing 11 is an arcuate curved surface that protrudesin the direction away from the casing 11 in the axial direction.

The spring support portion 78 protrudes toward the spring electrode 80from the first surface 75A of the protruding portion 75. The springsupport portion 78 has a surface facing the spring electrode 80. Thesurface of the spring support portion 78 includes a first flat surface78A, a second flat surface 78B, and an inclined surface 78C. Theinclined surface 78C connects the first flat surface 78A and the secondflat surface 78B. The first flat surface 78A and the second flat surface78B extend parallel with the base portion 71. The first flat surface 78Ais positioned farther from the base portion 71 than the second flatsurface 78B is from the base portion 71. The first flat surface 78A ispositioned closer to the casing 11 than the second flat surface 78B isto the casing 11. The inclined surface 78C extends from an edge of thefirst flat surface 78A farther from the casing 11. The inclined surface78C is connected to an edge of the second flat surface 78B closer to thecasing 11. The inclined surface 78C is inclined so that a downstreamedge of the inclined surface 78C in the direction away from the casing11 in the axial direction is positioned closer to the base portion 71than an upstream edge of the inclined surface 78C in the direction awayfrom the casing 11 in the axial direction is to the base portion 71.

The spring support portion 78 has a recessed portion 78D. The recessedportion 78D is recessed toward the base portion 71 in a center portionof each of the surfaces 78A, 78B, and 78Cin, where the center portion ofeach of the surfaces 78A, 78B, 78C is defined relative to the directionfrom the one end E10 of the casing 11 toward the other end E20 of thecasing 11. The recessed portion 78D is positioned between an edge of thefirst flat surface 78A closer to the casing 11 and an edge of the secondflat surface 78B farther from the casing 11. Further, the spring supportportion 78 has a side surface 78E closer to the casing 11. The springsupport portion 78 includes an engagement claw 78F positioned at theside surface 78E and protruding from the side surface 78E.

The through-hole 63A of the third cover portion 63 of the gear cover 60is formed to have a size corresponding to the spring electrode 80.

The spring electrode 80 is made of an electrically-conductive material.The spring electrode 80 is electrically connected to the developingroller 12. The spring electrode 80 is movable together with the cam 170.The spring electrode 80 includes a developing electrode 81 and a spring82. The developing electrode 81 has a shape in conformance with theshape of the spring support portion 78. The spring 82 is formedintegrally with the developing electrode 81.

The developing electrode 81 includes a first plate-like portion 81A, asecond plate-like portion 81B, a third plate-like portion 81C, a fourthplate-like portion 81D, and a fifth plate-like portion 81E. The firstplate-like portion 81A and the second plate-like portion 81B extendparallel with the base portion 71. The third plate-like portion 81Cconnects the first plate-like portion 81A and the second plate-likeportion 81B. The fourth plate-like portion 81D extends from an end ofthe first plate-like portion 81A closer to the casing 11 toward the baseportion 71. The fifth plate-like portion 81E extends from an end of thesecond plate-like portion 81B farther from the casing 11 toward the baseportion 71.

The first plate-like portion 81A, the second plate-like portion 81B, andthe third plate-like portion 81C are received by the recessed portion78D of the spring support portion 78 and are positioned at a bottomsurface of the recessed portion 78D.

In a state where the first plate-like portion 81A is positioned at thebottom surface of the recessed portion 78D, a surface of the firstplate-like portion 81A opposite to a surface thereof facing the cam 170is flush with the first flat surface 78A of the spring support portion78. In a state where the second plate-like portion 81B is positioned atthe bottom surface of the recessed portion 78D, a surface of the secondplate-like portion 81B opposite to a surface thereof facing the cam 170is flush with the second flat surface 78B of the spring support portion78. In a state where the third plate-like portion 81C is positioned atthe bottom surface of the recessed portion 78D, a surface of the thirdplate-like portion 81C opposite to a surface thereof facing the cam 170is flush with the inclined surface 78C of the spring support portion 78.

Alternatively, in a state where the first plate-like portion 81A ispositioned at the bottom surface of the recessed portion 78D, thesurface of the first plate-like portion 81A opposite to the surfacethereof facing the cam 170 is positioned farther from the base portion71 than the first flat surface 78A of the spring support portion 78. Ina state where the second plate-like portion 81B is positioned at thebottom surface of the recessed portion 78D, the surface of the secondplate-like portion 81B opposite to the surface thereof facing the cam170 is positioned farther from the base portion 71 than the second flatsurface 78B of the spring support portion 78. In a state where the thirdplate-like portion 81C is positioned at the bottom surface of therecessed portion 78D, the surface of the third plate-like portion 81Copposite to the surface thereof facing the cam 170 is positioned fartherfrom the base portion 71 than the inclined surface 78C of the springsupport portion 78. Further, the surface of the third plate-like portion81C inclined relative to the axial direction and opposite to the surfacethereof facing the cam 170 serves as a second cam surface 81G.

The second cam surface 81G has a fifth edge E105, and a sixth edge E106.The sixth edge E106 is positioned farther away from the casing 11 thanthe fifth edge E105 is from the casing 11 in the axial direction. Thesecond cam surface 81G is inclined so as to protrude toward the opening62A in a direction from the sixth edge E106 toward the fifth edge E105.

The fourth plate-like portion 81D and the fifth plate-like portion 81Einterpose the spring support portion 78 therebetween in the axialdirection. An engagement hole 81F engages with the engagement claw 78Fof the spring support portion 78. The fourth plate-like portion 81D hasthe engagement hole 81F.

The spring 82 includes a flat plate-like portion 82A, a first curvedportion 82B, and a second curved portion 82C. The flat plate-likeportion 82A extends parallel with the first plate-like portion 81A. Thefirst curved portion 82B is curved so as to protrude away from the cam170. The second curved portion 82C is curved so as to protrude towardthe casing 11. The flat plate-like portion 82A extends toward the casing11 from an end of the fourth plate-like portion 81D closer to the cam170. The first curved portion 82B is connected to an end of the flatplate-like portion 82A closer to the casing 11. The second curvedportion 82C extends from an end of the first curved portion 82B closerto the casing 11 in a direction away from the cam 170.

As illustrated in FIG. 13A, the spring 82 is positioned between the sidesurface 78E of the spring support portion 78 and the bearing 40. An endof the spring 82 closer to the casing 11 is in contact with the bearing40. The spring 82 urges the cam 170 in the direction away from thecasing 11 in the axial direction in a state where the cam 170 is at itsinitial position (i.e. the position illustrated in FIG. 13A). That is,the spring 82 urges the cam 170 from the initial position as an exampleof a first position toward an outside position as an example of a secondposition.

As illustrated in FIG. 11B, the rack gear 150 includes the main bodyportion 51, the rack gear portion 52, and a cam portion 55. The camportion 55 is not included in the rack gear 50 according to the firstembodiment, while the main body portion 51 and the rack gear portion 52of the rack gear 150 are similar to those of the rack gear 50 accordingto the first embodiment. The cam portion 55 is positioned at an upstreamportion of the rack gear 150 in a moving direction of the rack gear 150in an end portion of the main body portion 51 farther from the casing 11in the axial direction. In the following description, “upstream in themoving direction of the rack gear” and “downstream in the movingdirection of the rack gear” will also be simply referred to as“upstream” and “downstream”, respectively.

The cam portion 55 protrudes from the main body portion 51. A surface ofthe cam portion 55 closer to the casing 11 includes a first holdingsurface 55A, a second holding surface 55B, a third holding surface 55C,a connecting surface 55D, and a cam surface 55E. The first holdingsurface 55A, the second holding surface 55B, and the third holdingsurface 55C are planer surfaces orthogonal to the axial direction. Theconnecting surface 55D connects the first holding surface 55A and thesecond holding surface 55B. The cam surface 55E connects the secondholding surface 55B and the third holding surface 55C.

The first holding surface 55A and the third holding surface 55C arepositioned at positions the same as each other in the axial direction.The first holding surface 55A is positioned downstream relative to thethird holding surface 55C. The first holding surface 55A and the thirdholding surface 55C come into contact with the protrusion 77 to hold thecam 170 at the initial position (first position).

The second holding surface 55B is positioned between the first holdingsurface 55A and the third holding surface 55C in the moving direction ofthe rack gear 150. The second holding surface 55B is positioned fartheraway from the casing 11 than the first holding surface 55A is from thecasing 11 (see FIG. 12A). The second holding surface 55B comes intocontact with the protrusion 77 to hold the cam 170 at the outsideposition (second position).

The connecting surface 55D extends from an upstream edge of the firstholding surface 55A and is connected to a downstream edge of the secondholding surface 55B. The connecting surface 55D is inclined so that anupstream edge of the connecting surface 55D is positioned farther awayfrom the casing 11 than a downstream edge of the connecting surface 55Dis from the casing 11.

The cam surface 55E is inclined relative to the moving direction of therack gear 150. Specifically, the cam surface 55E extends from anupstream edge of the second holding surface 55B and is connected to adownstream edge of the third holding surface 55C. The cam surface 55E isinclined so that an upstream edge of the cam surface 55E is positionedcloser to the casing 11 than a downstream edge of the cam surface 55E isto the casing 11.

In this embodiment, as illustrated in FIG. 12A, in a case where thedeveloping cartridge 1 is in a brand-new state, the cam 170 is at itsinitial position since the protrusion 77 of the cam 170 is supported atthe first holding surface 55A of the rack gear 150. Specifically, anurging force applied to the cam 170 from the spring electrode 80 isreceived by the first holding surface 55A.

In a case where the developing cartridge 1 is attached to the main bodycasing of the image forming apparatus in a state where the cam 170 is atthe initial position, the actuator AC is pushed by the second plate-likeportion 81B of the spring electrode 80 supported at the cam 170 asillustrated in FIG. 13A. As a result, the actuator AC swingably movesfrom a first posture to a second posture. The optical sensor detects thechange in posture of the actuator AC. At this time, the electrode of theactuator AC and the spring electrode 80 are electrically connected toeach other.

Thereafter, as illustrated in the sequence of FIGS. 12A and 12B, in acase where the driving force is transmitted to the agitator gear 31, therack gear 150 moves in the direction from the one end E10 of the casing11 toward the other end E20 of the casing 11. In a case where the firstholding surface 55A separates from the protrusion 77 in accordance withthe movement of the rack gear 150, the cam 170 moves in the directionaway from the casing 11 in the axial direction due to the urging forceof the spring electrode 80. Thereafter, in a case where the protrusion77 comes into contact with the second holding surface 55B, the movementof the cam 170 is stopped, and the cam 170 is placed at the outsideposition farther away from the casing 11 than the initial position fromthe casing 11.

While the cam 170 moves from the initial position to the outsideposition, the actuator AC is pushed by the inclined third plate-likeportion 81C of the spring electrode 80 supported at the cam 170 asillustrated in FIG. 13B. As a result, the actuator AC swingably movesfrom the second posture to a third posture, and the optical sensordetects the change in posture of the actuator AC.

Thereafter, as illustrated in the sequence of FIGS. 12B and 12C, in acase where the rack gear 150 further moves in the direction from the oneend E10 of the casing 11 toward the other end E20 of the casing 11, thecam 170 returns to the initial position from the outside position sincethe protrusion 77 is pushed by the cam surface 55E of the rack gear 150in the direction toward the casing 11 in the axial direction against theurging force of the spring electrode 80. As a result, the actuator ACswingably moves from the third posture to the second posture asillustrated in FIG. 13A, and the optical sensor detects the change inposture of the actuator AC.

As described above, in the second embodiment, similarly to the firstembodiment, meshing between the rack gear 150 and the agitator gear 31can be released since the rack gear 150 moves in the direction from theone end E10 of the casing 11 toward the other end E20 of the casing 11.Further, in the second embodiment, since the spring 82 and thedeveloping electrode 81 are configured as a single component (springelectrode 80), the number of components can be reduced. The spring andthe developing electrode may be separate components. Further, the springas a separate component may be a coil spring or a wire spring.

<Modifications>

While the description has been made in detail with reference to theembodiments thereof, it would be apparent to those skilled in the artthat many modifications and variations may be made therein withoutdeparting from the scope of the disclosure.

In the first embodiment, the fourth cam surfaces 24A are provided at thedeveloping electrode 20, and the second cam surfaces 76A are provided atthe cam 70. However, for example, a protrusion engaging with the secondcam surface of the cam may be provided at the developing electrode.

In the first embodiment, the rack gear 50 in its entirety is coveredwith the gear cover 60. However, the gear cover may cover a portion ofthe rack gear and may expose the remaining portion of the rack gear tooutside.

In the first and second embodiments, the agitator gear 31 is exemplifiedas an example of a gear. However, any gears other than the agitator gear31 may be available.

In the first and second embodiment, the compression coil spring SP andthe spring 82 are exemplified as a spring. However, the spring may be,for example, a wire spring or a torsion spring.

In the first embodiment, the cam 70 is movably supported at the gearcover 60. However, the cam may be movably supported at the casing.

Further, the respective elements described in the above embodiments andmodifications may be arbitrarily combined and implemented.

What is claimed is:
 1. A developing cartridge comprising: a casingconfigured to accommodate toner therein; a developing roller rotatableabout a first axis extending in an axial direction, the developingroller being positioned at one end of the casing; a developing electrodeelectrically connected to the developing roller; a gear rotatable abouta second axis parallel with the first axis; a rack gear meshing with thegear, the rack gear being movable in a direction from the one end of thecasing toward another end of the casing opposite to the one end of thecasing, the rack gear including a protrusion; and a cam movable from afirst position to a second position, the second position being fartheraway from the casing than the first position is from the casing in theaxial direction, the cam having: a first cam surface contacting theprotrusion in a case where the cam is at the first position, the firstcam surface causing the cam to move from the first position to thesecond position in a case where the rack gear moves in the directionfrom the one end of the casing toward the another end of the casing in astate where the first cam surface is in contact with the protrusion; anda second cam surface moving the developing electrode in a direction awayfrom the cam while contacting the developing electrode in a case wherethe cam moves from the first position to the second position, thedirection away from the cam being a direction different from a movingdirection of the rack gear and a moving direction of the cam.
 2. Thedeveloping cartridge according to claim 1, further comprising a springfor electrically connecting the developing electrode to the developingroller.
 3. The developing cartridge according to claim 2, furthercomprising a bearing for supporting the developing roller, wherein thespring has: one end in contact with the developing electrode; andanother end opposite to the one end of the spring, the another end beingin contact with the bearing.
 4. The developing cartridge according toclaim 3, wherein, in a state where the one end of the spring is incontact with the developing electrode and the another end of the springis in contact with the bearing, the spring has a length smaller than anatural length of the spring.
 5. The developing cartridge according toclaim 3, wherein the bearing is made of an electrically-conductiveresin.
 6. The developing cartridge according to claim 1, wherein thedeveloping electrode is made of an electrically-conductive resin.
 7. Thedeveloping cartridge according to claim 1, wherein the first cam surfacehas: a first edge; and a second edge positioned farther away from thecasing than the first edge is from the casing in the axial direction,and wherein the first cam surface is inclined so that the first edge ispositioned downstream relative to the second edge in the movingdirection of the rack gear.
 8. The developing cartridge according toclaim 1, wherein the cam has a third cam surface positioned downstreamrelative to the first cam surface in the moving direction of the rackgear, the third cam surface contacting the protrusion in a case wherethe cam is at the second position, and wherein the third cam surfacecauses the cam to move from the second position to the first position ina case where the rack gear moves in the direction from the one end ofthe casing toward the another end of the casing in a state where thethird cam surface is in contact with the protrusion.
 9. The developingcartridge according to claim 8, wherein the third cam surface has: athird first edge; and a fourth second edge positioned farther away fromthe casing than the third first edge is from the casing in the axialdirection, and wherein the third cam surface is inclined so that thefourth second edge of the third cam surface is positioned downstreamrelative to the third first edge of the third cam surface in the movingdirection of the rack gear.
 10. The developing cartridge according toclaim 8, wherein the first cam surface is positioned at a positiondifferent from the third cam surface in the moving direction of the cam.11. The developing cartridge according to claim 1, further comprising:an agitator configured to agitate toner accommodated in the casing; andan agitator gear mounted to an end portion of the agitator and rotatabletogether with the agitator, wherein the agitator gear serves as thegear.
 12. The developing cartridge according to claim 1, furthercomprising a coupling positioned opposite to the developing electroderelative to the casing.
 13. The developing cartridge according to claim1, wherein the developing gear has a fourth further cam surfacecontacting the second cam surface and extending parallel with the secondcam surface.
 14. The developing cartridge according to claim 1, whereinthe rack gear includes: a main body portion having a plate shape andextending in the moving direction of the rack gear; and a plurality ofgear teeth meshing with the gear, and wherein the plurality of gearteeth and the protrusion protrude from the main body portion and arepositioned at positions different from each other in the movingdirection of the rack gear.
 15. The developing cartridge according toclaim 14, wherein the protrusion is positioned at a position differentfrom the plurality of gear teeth in the axial direction.
 16. Thedeveloping cartridge according to claim 1, wherein the second camsurface has: a fifth first edge; and a sixth second edge positionedfarther away from the casing than the fifth first edge of the second camsurface is from the casing in the axial direction, and wherein thesecond cam surface is inclined so as to protrude toward the developingelectrode in a direction from the sixth second edge of the second camsurface toward the fifth first edge of the second cam surface.
 17. Adeveloping cartridge comprising: a casing configured to accommodatetoner therein; a developing roller rotatable about a first axisextending in an axial direction, the developing roller being positionedat one end of the casing; a gear rotatable about a second axis extendingin the axial direction; a developing electrode electrically connected tothe developing roller; a rack gear movable from the one end of thecasing toward another end of the casing opposite to the one end of thecasing, the rack gear being movable in a direction from the one end ofthe casing toward the another end of the casing in accordance withrotation of the gear by meshing with the gear, the rack gear including aprotrusion; a cover covering at least a portion of the rack gear, thecover having an opening through which the developing electrode isexposed to an outside; and a cam movable from a first position to asecond position, the second position being farther away from the casingthan the first position is from the casing in the axial direction, thecam having: a first cam surface having a first edge and a second edge,the second edge being positioned farther away from the casing than thefirst edge is from the casing in the axial direction, the first camsurface being inclined so that the first edge is positioned downstreamrelative to the second edge in a moving direction of the protrusion, thefirst cam surface causing the cam to move from the first position to thesecond position by engaging with the protrusion, the first cam surfacebeing positioned outside of a movement locus of the protrusion in a casewhere the cam is at the second position; and a second cam surfacemovable together with the first cam surface, the second cam surfacebeing positioned farther away from the casing than the first cam surfaceis from the casing in the axial direction, the second cam surface beingmovable while contacting the developing electrode, the second camsurface having a fifth first edge and a sixth second edge, the sixthsecond edge of the second cam surface being positioned farther away fromthe casing than the fifth first edge of the second cam surface is fromthe casing in the axial direction, the second cam surface being inclinedso as to protrude toward the opening in a direction from the sixthsecond edge of the second cam surface toward the fifth first edge of thesecond cam surface.
 18. The developing cartridge according to claim 17,further comprising a spring for electrically connecting the developingelectrode to the developing roller.
 19. The developing cartridgeaccording to claim 17, wherein the cam further includes a third camsurface positioned downstream relative to the first cam surface in amoving direction of the rack gear, the third cam surface beingpositioned within the movement locus of the protrusion in a case wherethe cam is at the second position, wherein the third cam surface has: athird first edge; and a fourth second edge positioned farther away fromthe casing than the third first edge of the third cam surface is fromthe casing in the axial direction, and wherein the third cam surface isinclined so that the fourth second edge of the third cam surface ispositioned downstream relative to the third first edge of the third camsurface in the moving direction of the rack gear.
 20. A developingcartridge comprising: a casing configured to accommodate toner therein;a developing roller rotatable about a first axis extending in an axialdirection, the developing roller being positioned at one end of thecasing; a gear rotatable about a second axis parallel with the firstaxis; a rack gear meshing with the gear, the rack gear being movable ina direction from the one end of the casing toward another end of thecasing opposite to the one end of the casing; a cam movable from a firstposition to a second position, the second position being farther awayfrom the casing than the first position is from the casing in the axialdirection, the cam including a protrusion; a spring urging the cam fromthe first position toward the second position; a cover having anopening; and a developing electrode electrically connected to thedeveloping roller, the developing electrode being movable together withthe cam, the developing electrode having a second cam surface, thesecond cam surface having a fifth first edge and a sixth second edge,the sixth second edge being positioned farther away from the casing thanthe fifth first edge is from the casing in the axial direction, thesecond cam surface being inclined so as to protrude toward the openingin a direction from the sixth second edge toward the fifth first edge,the rack gear having: a first holding surface contacting the protrusionto hold the cam at the first position; and a second holding surfacecontacting the protrusion to hold the cam at the second position. 21.The developing cartridge according to claim 20, wherein the developingelectrode is formed integrally with the spring.
 22. A developingcartridge comprising: a casing configured to accommodate toner therein;a developing roller rotatable about a first axis extending in an axialdirection, the developing roller being positioned at a first end of thecasing; a developing electrode electrically connected to the developingroller; a gear rotatable about a second axis parallel with the firstaxis; a rack gear meshing with the gear, the rack gear being movable ina direction extending between the first end of the casing and a secondend of the casing opposite to the first end of the casing, the rack gearincluding a protrusion; and a cam movable between a first position and asecond position, the cam having: a first cam surface configured toengage the protrusion to selectively move the cam between the first andsecond positions in response to movement of the rack gear.
 23. Thedeveloping cartridge according to claim 22, wherein the rack gear ismovable in a direction extending from the first end of the casing to thesecond end of the casing to move the cam from the first position to thesecond position.
 24. The developing cartridge according to claim 22,wherein the cam further includes a second cam surface that moves thedeveloping electrode in a direction away from the cam in response to themovement of the cam from the first position to the second position. 25.The developing cartridge according to claim 22, wherein the secondposition is farther away from the casing than the first position is fromthe casing in the axial direction.
 26. The developing cartridgeaccording to claim 22, wherein the cam is configured to move thedeveloping electrode in a direction away from the cam in response to themovement of the cam from the first position to the second position, thedirection away from the cam being a direction different from a movingdirection of the rack gear and a moving direction of the cam.
 27. Adeveloping cartridge comprising: a casing configured to accommodatetoner therein; a developing roller rotatable about a first axisextending in an axial direction, the developing roller being positionedat a first end of the casing; a developing electrode electricallyconnected to the developing roller; a gear rotatable about a second axisparallel with the first axis; a rack gear meshing with the gear, therack gear including a protrusion; and a cam movable from a firstposition to a second position, the cam having a first cam surfacecontacting the protrusion in a case where the cam is at the firstposition, the first cam surface causing the cam to move from the firstposition to the second position in a case where the rack gear moves in adirection extending between the first end of the casing and a second endof the casing opposite to the first end of the casing.
 28. Thedeveloping cartridge according to claim 27, wherein the protrusioncontacts the first cam surface as the rack gear moves in the directionextending from the first end of the casing toward the second end of thecasing.
 29. The developing cartridge according to claim 27, wherein thesecond position is farther away from the casing than the first positionis from the casing in the axial direction.
 30. The developing cartridgeaccording to claim 27, wherein the cam further includes a second camsurface moving the developing electrode in a direction away from the camwhile contacting the developing electrode in a case where the cam movesfrom the first position to the second position, the direction away fromthe cam being a direction different from a moving direction of the rackgear and a moving direction of the cam.
 31. A developing cartridgecomprising: a casing configured to accommodate toner therein; adeveloping roller rotatable about a first axis extending in an axialdirection, the developing roller being positioned at one end of thecasing; a developing electrode electrically connected to the developingroller; a gear rotatable about a second axis parallel with the firstaxis; a rack gear meshing with the gear and being movable in a directionextending between the one end of the casing and another end of thecasing opposite the one end of the casing; and a cam movable from afirst position to a second position, the cam being movable from thefirst position to the second position to move the developing electrodein a case where the rack gear moves in the direction extending betweenthe one end of the casing and the another end of the casing opposite tothe one end of the casing.
 32. The developing cartridge according toclaim 31, wherein the rack gear includes a protrusion and the camincludes a cam surface, the cam surface being contacted by theprotrusion to cause the cam to move from the first position to thesecond position in a case where the rack gear moves in the directionbetween the one end of the casing and the another end of the casingopposite to the one end of the casing.
 33. The developing cartridgeaccording to claim 32, wherein the cam surface moves the developingelectrode in a direction away from the cam in a case where the cam movesfrom the first position to the second position.
 34. The developingcartridge according to claim 31, wherein the second position is fartheraway from the casing than the first position is from the casing in theaxial direction.
 35. The developing cartridge according to claim 31,wherein the cam further includes a cam surface configured to move thedeveloping electrode in a direction away from the cam while contactingthe developing electrode in a case where the cam moves from the firstposition to the second position, the direction away from the cam being adirection different from a moving direction of the rack gear and amoving direction of the cam.